1. Field of the Invention
The present invention relates generally to a photoelectric sensor. More particularly, the present invention relates a photoelectric sensor for detecting an object within a predetermined detection area, and provides an enable signal for enabling operation of a target apparatus and a disable signal for disabling the operation of the target apparatus based on the result of the detection.
2. Description of Related Art
There have been known safety systems for setting an object detection area around a target apparatus such as machine tools and industrial robots. Such safety systems detect objects, for example workers or operators, in the predetermined detection area to interrupt a motion of the target machine, or otherwise disable operation of the target apparatus to provide a safe area around the target. Some of the safety systems have photoelectric sensors used as detectors for detecting an object around the target apparatus. Such photoelectric sensors emit a light beam toward a predetermined measurement area to scan an object detection area and receive a scanning light beam reflected by an object located in the measurement area, thereby detecting the presence or the absence of an object within the object detection area based on a signal representing an intensity of the reflected scanning light beam.
Japanese Laid-Open Patent No. H04-310890 describes a system, which is installed in a vehicle, for setting a measurement area around a vehicle which is the target apparatus, and for displaying a position of an external object such as a bicycle and the like on a display device when detecting the external object within the measurement area set around the vehicle. This system optically scans the measurement areas on the rear and the left of the vehicle, and shows a position of the bicycle or the like within the measurement area on the display device so as to provide secured safety to the vehicle against possible accidents when the system receives the reflected scanning light from the bicycle or the like within the measurement area. The system may take the form of an optical scanning device housed in a barrel casing as described, for example, in Japanese Laid-Open Patent H03-175390.
The above conventional optical scanners have the risk of failing to detect an object even if the object is present within an intended measurement area in the case where a preset measurement area, i.e. a scanning area of the optical scanner, does not match the intended measurement area due to an accidental incorrect disposition of the optical scanner or an accidental incorrect attitude of the optical scanner. In such a case, an area which is not covered by the measurement area, is present. As a result, the optical scanner can not detect an object to be detected in the uncovered area even though the object is present in the intended measurement area.